Gram-positive bacteria of the species Bacillus thuringiensis produce proteinaceous crystals that are lethal to a number of insects including agricultural insect pests (Table 1). Reviews are available detailing the microbiology, toxicology and molecular genetics of Bacillus thuringiensis including: Sommerville (1973) Ann. N.Y. Acad. Sci. 217:93-103; Rogoff and Yousten (1969) Ann. Rev. Microbiol. 23:357-389; Bulla et al. (1975) Ann. Rev. Microbiol. 29:163-190; Dulmage (1981) in Microbial Control of Pests and Plant Diseases, Burges (ed.), Academic Press, London, pp. 193-222; Aronson et al. (1986) Microbiol. Rev. 50:1-24.
A number of subspecies of Bacillus thuringiensis (Table 2) have been described which produce crystal proteins toxic to lepidopteran, dipteran or coleopteran insects. The crystals are parasporal, forming during sporulation, within the cell. Bacillus thuringiensis varieties display varying spectra of activity. Many subspecies, for example kurstaki strains, are toxic primarily for lepidopterans. The crystals of these subspecies contain a non-toxic protoxin of 130-140 kd molecular weight. This protoxin is solubilized and degraded to a toxic polypeptide (about 68 kd molecular weight) in the mid-gut of susceptible insects. The protoxin can also be solubilized and activated by protease treatment, in vitro. Several subspecies, particularly israelensis strains, display selective insecticidal activity toward Diptera (i.e., mosquitoes or black flies). Dipteran toxic protein appears to be distinct from the kurastaki crystal protein, having different overall amino acid composition and being immunologically distinct. The major component of crystals of israelensis strains has been reported to be a 26-28 kd protein, a 65 kd protein, or most recently a 130 kd protein (Hurley et al. (1985) Biochem. Biophys. Res. Comm. 126:961-965; Ward et al. (1984) FEBS Lett. 175:377-382; and Armstrong et al. (1985) J. Bacteriol. 161:39-46; Visser et al. (.+-.1986) FEMS Microbiology Let. 33:211-214). The mosquitocidal toxin found in some kurstaki subspecies is reported to be a 65 kd protein (Yamamoto and McLoughlin (1981) Biochem. Biophys. Res. Comm. 103:414-421) and is believed to be distinct from the israelensis mosquitocidal protein. Two Bacillus thuringiensis variants (Krieg et al. (1983) Z. Ang. Ent. 96:500-508 ; Krieg et al. (1984) Ang. Schadlingskde. Pflanzenschutz, Univeltschutz 57:145-150; and Herrnstadt et al. (1986) Biotechnology 4:305-308) have recently been described which display toxicity for Coleoptera rather than Lepidoptera. Crystals of one of these varieties, designated san diego, are reported to have a major protein component of about 64 kd. No higher molecular weight precursor was identified in gels of crystal components; however, an 83 kd protein is reported to be expressed by san diego CP genes cloned in Escherichia coli. The coleopteran toxin does not cross react with antiserum raised to lepidopteran specific strains kurstaki HD-1 or HD-73, and there is little peptide homology between the coleopteran toxin and HD-73 protein. It is not as yet known whether protoxins are degraded to produce these toxic proteins in the cases of the dipteran and coleopteran specific toxins.